Hitherto, as disclosed in Patent Document 1 below, there is known a drive device of this type which includes a vertical high-temperature tank (storing a high-temperature liquid) and a vertical low-temperature tank (storing a low-temperature liquid) having bottom portions thereof communicating with each other. Here, a plurality of bag-shaped floating pieces are attached to an endless floating piece support member extending from the vertical high-temperature tank to the vertical low-temperature tank and each floating piece stores a heat medium which becomes a gas state in the vertical high-temperature tank and becomes a liquid state in the vertical low-temperature tank.
According to the drive device of the related art, the heat medium stored in the bag-shaped floating piece becomes expanded in the gas state at the vertical high-temperature tank so as to generate buoyancy and becomes contracted in the liquid state at the vertical low-temperature tank. Accordingly, the endless floating piece support member is rotated by the buoyancy generated at the vertical high-temperature tank.